3<3 DESCRIPTION OF PLATES. 



PX.ATB VI. 

 Tenebrio molitor. 



FIGS. 169-70. Equatorial plates of spermatogonial mitosis, showing 19 large and 



i small chromosome. 



I7 I - I 75- Condensation stage, bouquet stage, spireme stage, and rather rare 

 tetrad stage of young spermatocyte. 



176. Bivalent chromosomes, with longitudinal split; small chromosome 



shown at s. 



177. Bivalent chromosomes condensed into a close spireme. 



178-179. Bivalent chromosomes separating for mitosis. The unsymmetrical 

 pair shown in fig. 179. 



180. Prophase of first maturation mitosis, showing the unsymmetrical 



pair and the tetrad nature of the symmetrical pairs. 



181. Prophase of same mitosis, showing symmetrical and unsymmetrical 



pairs, as in figs. 178 and 179. 



182. Metaphase, unsymmetrical pair out of the equatorial plane. 



183. Tangential section of a spindle in metaphase, showing the unsym- 



metrical pair and one symmetrical pair. 



184. Equatorial plate of same mitosis, 10 chromosomes. 



1840. Early anaphase, showing separation of the elements of the unsym- 

 metrical pair. 



185. Later anaphase. 



186. Polar plate, showing 9 large and i small chromosome. 



187. Polar plate, showing 10 large chromosomes. 



188. Condensation stage between the two maturation divisions. 

 189-190. Prophase of second maturation division, fig. 189 showing 10 equal 



dyads, and fig. 190, showing 9 equal and I small dyad. 



191. Equatorial plate, showing i small chromosome and 9 large ones. 



192. Equatorial plate, showing 10 large chromosomes. 

 I93- I 94- Tangential sections of spindle in metakinesis. 



195. Anaphase of same mitosis. 



196. Polar plates of a spindle, showing in each i small chromosome and 



9 large ones. 



197. Polar plates of another spindle, 10 large chromosomes in each. 



198. Young spermatid, showing isolated small chromosome. 



199. Young spermatid, showing isolated large chromosome and rotation 



of nuclear contents. 

 200-2020, b. Older spermatids. 



203. Sperm-heads, showing centrosome and granular chromatin. 



204. Equatorial plate from dividing somatic cell of male pupa, showing 



19 large and I small chromosome. 



205-206. Daughter plates of a similar spindle, showing small chromosome 

 in each ; three of the large chromosomes missing in 206. 



207. Equatorial plate of a dividing cell of follicle of a young egg, show- 



ing 20 large chromosomes. 



208. Prophase of mitosis in a young oogonium, showing 20 large chro- 



mosomes in two sections, a and b. 



